The present invention relates to a method of operating a reciprocating piston internal combustion engine and more particularly, to a method of verifying cold start spark retard in a reciprocating piston internal combustion engine.
To limit CO2, NOx and other gaseous emissions, most vehicles are equipped with a catalytic converter. A chemical catalyst (typically a rare earth metal) of a catalytic converter is not fully operational until it reaches a temperature range of between 700xc2x0 F. and 800xc2x0 F. Accordingly, when a vehicle is initially starting, the catalytic converter will not be fully warmed and its efficiency will be reduced. Typically, the catalytic converter reaches operating temperature (commonly referred to as light off temperature) in approximately 90 seconds of normal operation of the vehicle engine.
To further reduce emissions from a vehicle engine, it is desirable to heat the catalytic converter catalyst when the engine starts from a cold start at a quicker pace so that it more readily reaches its optimum temperature. One method to preheat the catalyst is to retard the spark in the engine cylinders. Retarding the spark in the cylinder causes a less complete combustion and therefore places more CO2 within the engine exhaust. The increased CO2 within the engine exhaust is oxidized within the catalytic converter causing the catalyst to heat at a faster rate.
An engine controller will typically only command a cold start spark retard when certain conditions are met. If the vehicle has been sitting for a prolonged period of time, the controller will cause the starting operation of the engine to have a retard operation. To determine if the engine is cold, typically the controller will rely on an engine coolant temperature sensor. In situations when the engine does not employ spark retard during a cold start, a vehicle operator is alerted that their engine emission control system is not functioning in an optimum desired manner. The alert is usually a message displayed on the instrument panel, such as xe2x80x9ccheck engine.xe2x80x9d
The engine control system has a series of spark drivers which deliver a voltage charge to a primary coil. However, the timing of spark within the combustion chamber is also dependent upon a discharge of a secondary coil. Therefore, spark retard cannot be confirmed by comparing a crankshaft angular positional sensor signal with a signal output provided by a spark driver. Accordingly, to monitor the exact timing of a spark within a cylinder requires instrumentation which is impractical for a production vehicle. It is therefore desirable to provide confirmation of spark retard in a manner that is set free from a reliance upon ignition system electrical datum.
To make manifest the above noted and other desires, a revelation of the present invention is brought forth.
In one preferred method of the present invention, an engine emission control system utilizes crankshaft acceleration to monitor cold start spark retard. The present invention utilizes a variance in a crankshaft acceleration based deviation signal and looks for changes in the variance to confirm if cold spark retard has occurred by the ignition system.
In a second preferred method of the present invention, a threshold level of a group of cylinder crankshaft acceleration deviation signals can be detected and compared to a level of crankshaft deviation acceleration when normal spark is commanded to determine if commanded spark retard has been realized.
Other features of the invention will become more apparent to those skilled in the art from a reading of the following description and upon reference to the drawings.